Synthetic fibers are made from polymers by melting the polymer and drawing it through a spinneret which contains tiny openings. The polymer usually contains gels, unusually high molecular weight polymer material, and solid particles of contamination. The gels and particles must be removed prior to spinning. If either the gels or solid particles are not removed, they can clog the openings of the spinneret or cause weak points in the fiber, resulting in fiber breakage.
Contaminants, including gels, are removed by passing the polymer through a filter medium which includes sintered metal fibers. Preferably, several layers of fibers having different diameters are employed. This provides layers of differing porosity. These layers are stacked upon each other to provide a structure where the pores decrease in size along the flow path of the polymer.
One problem with this conventional filter medium is that it trends to be clogged with gels or solid particles. The gels tend to extrude through larger, upstream pores. As they encounter smaller pores, the gels are broken apart into small fragments which eventually clog the tiny downstream pores of the filter medium. Normally, the on-stream life of the conventional filter medium ranges between 300 and 4,000 pounds of polymer flow per cubic inch of medium, depending upon the type of polymer being filtered and filtration conditions. This on-stream life could be extended if the filter medium had a greater contaminant holding capacity.